Ultrafine MnO2 Research Articles

Laser-induced transient conversion of rhodochrosite/polyimide into multifunctional MnO2/graphene electrodes for energy storage applications

Laser-induced graphene (LIG) has been extensively investigated for electrochemical energy storage due to its easy synthesis and highly conductive nature. However, the limited charge accumulation in LIG usually leads to significantly low energy densities. In this work, we report a novel strategy to directly transform natural rhodochrosite into ultrafine manganese dioxide (MnO2) nanoparticles (NPs) in the polyimide (PI) substrate for high-performance micro-supercapacitors (MSCs) and lithium-ion batteries (LIBs) through a scalable and cost-effective laser processing method. Specifically, laser treatment on rhodochrosite/polyimide precursors induces the thermal explosion, which splits rhodochrosite (10 μm) into MnO2 NPs (12–16 nm) on the carbon matrix of LIG due to the sputtering effect. Benefiting from largely exposed active sites from the ultrafine MnO2 and the synergetic effect from highly conductive LIG, the MnO2/LIG MSCs show a high specific capacitance of 544.0 F g−1 (154.3 mF cm−2; 14.16 F cm−3) at 3 A/g and 82.1% capacitance retention after 10,000 cycles at 5A/g, in contrast to pure LIG (<100 F g−1). Moreover, the MnO2/LIG-based LIBs show the highest reversible discharge capacity of ∼1097 mAh g−1 at 0.2 A/g and ∼ 866.4 mAh g−1 at 1.0 A/g. This study opens a new route for synthesizing novel LIG-based composites from natural minerals.

Facile Synthesis of Ultrafine and Highly Dispersible MnO2 Nanoparticles for Energy Storage in Supercapacitors

AbstractManganese dioxide (MnO2) has been extensively investigated as an electrode material for supercapacitors because of its high theoretical capacitance, great abundance, and low toxicity. To obtain satisfactory capacitance performance, in recent years, many efforts have been dedicated to the fabrication of MnO2 nanoparticles that offer a larger specific surface area and an escalated chemical activity. Beyond them, the ideal dispersibility of nanoparticles in a liquid medium is also of vital importance when processing those powdery materials into slurry ones for some particular uses, such as editable and ink‐printing supercapacitor devices. In this study, the as‐synthesized ultrafine MnO2 nanoparticles having excellent dispersibility in water can be prepared via a facile one‐step hydrothermal route, with a uniform size in diameter of 200 nm exhibiting a large specific surface area of ~389.7 m2 g−1, and a high specific capacitance of 135.7 F g−1 at 5 mV s−1.

Carbon nanofibers enabling manganese oxide cathode superior low temperature performance for aqueous zinc-ion batteries

Mn-based aqueous zinc-ion batteries are potential candidates for energy storage owing to the low cost, high efficiency, and safety. Nevertheless, the Jahn–Teller effect induces Mn2+ dissolution and irreversible phase changes, seriously deteriorating the cycling life. Herein, the facile construction and low temperature performance of the core–shell composites of polyimide derived nitrogen-doped carbon nanofibers and δ-MnO2 (δ-MnO2-CNFs) are reported, where ultrafine MnO2 arrays are tightly anchored on carbon nanofibers. The hybrid effect of nitrogen doping, porous structure, and abundant active sites effectively inhibits the structural damage of MnO2. The as-prepared δ-MnO2-CNFs cathode achieves a high specific capacity of 232.9 mAh g−1 and energy density of 450.7 Wh kg−1 at a current density of 100 mA g−1, and could be stably cycled for 500 cycles at a high current rate of 1 A g−1. The density functional theory calculation results show that the synergistic effect in δ-MnO2-CNFs is more conducive to the transfer of zinc ions. Furthermore, a salty ice electrolyte Zn(ClO4)2 has been used for the Zn//δ-MnO2-CNFs cell, which can work at a low temperature of −20 °C, and a stable low temperature (0 °C) cycle of 500 cycles is achieved at 1 A g−1.

Double-network aerogel-derived spongy 3D porous MnO/C composite for lithium-ion batteries with increasing capacity

The uneven dispersion of MnO easily leads to local volume change, resulting in the crushing and pulverizing of electrode. Herein, a spongy three-dimensional (3D) porous MnO/C composite was fabricated by pyrolysis of the double-network (DN) aerogel composed of agar (AG) and Mn-crosslinked sodium alginate (SA). The spongy MnO/C composite has homogeneous distribution and uniform size ultrafine MnO nanoparticles embedded into 3D porous carbon network and shows high BET surface area of 363 m2 g−1, which can not only improve the electrical conductivity, but effectively confine the expulsion of MnO and restrain the crushing and pulverizing of electrode. As anode for LIBs, the spongy MnO/C composite exhibits superior rate capability (574 mAh g−1, 2 A g−1) and excellent cycling stability. The capacity gradually increases during the cycling process, reaching 1270 mAh g−1 after 500 cycles at 2 A g−1. The rising capacity can be attributed to the following reasons: 1) more Mn2+ was oxidated to higher valence, 2) The enhanced amorphism of MnO improves Li+ diffusion kinetics, 3) the reversible form and decomposition of SEI.

Cyclically formed dual mechanical/functional interface stabilizing silicon with enhanced lithium complementary effect

Silicon has been focused as a potential candidate in practical lithium-ion batteries due to its amiable feature of high theoretical specific capacity and environmental friendliness. However, its long-term stability requires further improvements for the significant volumetric expansion during lithium insertion. A novel strategy of a complementary effect created by the special extra lithium-storage capability of transition metal oxides is proposed and explored for the modification of silicon in the study. Si@MnO/C composite with highly compact structure is thus prepared by a facile electrostatic process combined with heat treatment. The results demonstrate that the strategical introduction of ultrafine MnO plays a crucial role in the generation of the complementary effect, which outstandingly enhances the durability as well as the kinetics of silicon anode. A reversible capacity of 1085.7 mAh g−1 with a Coulombic efficiency over than 99% has been obtained after 500 cycles at the current density of 200 mA g−1. Even at a high current density of 2000 mA g−1, a retention capacity of 946.3 mAh g−1 could be maintained after 920 cycles.

Classification of Ultrafine Particles Using a Novel 3D-Printed Hydrocyclone with an Arc Inlet: Experiment and CFD Modeling.

Ultrafine particle classification can be realized using hydrocyclones with novel structures to overcome the limitations of conventional hydrocyclones with tangential inlets or cone structures. Herein, the hydrocyclones with different inlet structures and cone angles were investigated for classifying ultrafine particles. Computational fluid dynamics (CFD) simulations were performed using the Eulerian-Eulerian method, and ultrafine MnO2 powder was used as a case study. The simulation results show a fine particle (≤5 μm) removal efficiency of 0.89 and coarse particle (>5 μm) recovery efficiency of 0.99 for a hydrocyclone design combining an arc inlet and a 30° cone angle under a solid concentration of 2.5 wt %. Dynamic analysis indicated that the novel arc inlet provided a preclassification effect to reduce the misplacement of fine/coarse particles, which cannot be provided by conventional tangential or involute inlets. Furthermore, the proposed design afforded comprehensive improvement in the flow field by regulating the residence time and radial acceleration. Subsequently, a novel hydrocyclone with an arc inlet and 30° cone angle was manufactured using the three-dimensional (3D) printing technology. Experiments were conducted for classifying ultrafine MnO2 particles using the novel 3D-printed hydrocyclone and conventional hydrocyclone. The results demonstrate that the classification performance of the 3D-printed hydrocyclone was superior to that of the conventional one, in particular, the removal efficiency of fine particles from 0.719 to 0.930 using a 10 wt % feed slurry.

Room-temperature catalytic removal of indoor trace hexanal by weakly crystallized MnO2 ultrafine nanowires

Aldehydes besides formaldehyde are ubiquitous in indoor environment and pose great threats to human health, however few efforts have been made to catalytically decompose them at room temperature. Here, weakly crystallized ultrafine MnO2 nanowires (φ ∼ 5 nm) were hydrothermally synthesized for decomposing hexanal-a frequently detected indoor odorant. As-synthesized ultrafine nanowires were assembled into three-dimensional porous structure, which is conducive to expose active sites. Due to its high specific surface area, abundant oxygen vacancies and ability to generate superoxide radicals at room temperature, as-synthesized ultrafine nanowire MnO2 not only realized fast complete oxidation of 15 ppm hexanal at temperature significantly lower than that required by catalysts reported in literatures, but also exhibited excellent room-temperature catalytic activity for ppb-level hexanal removal. Though trace acetic acid was released as major intermediate during hexanal decomposition, this work first demonstrates it is feasible to catalytically remove aldehydes besides formaldehyde at room temperature.

Cover Image

The cover image is based on the Research Article Improved-quality graphene film decorated with ultrafine MnO2 nanoparticles as a multifunctional current collector for high-reversibility zinc-ion batteries by Young-Geun Lee et al., https://doi.org/10.1002/er.7624.

Mechanisms of U(VI) removal by biochar derived from Ficus microcarpa aerial root: A comparison between raw and modified biochar

Uranium (U) is a toxic and radioactive element. Excessive amounts of aqueous U(VI) generated from U mining, processing and nuclear industry may result in severe and irreversible damage to the environment. Herein, Ficus microcarpa aerial root (FMAR), a biowaste material, was used to adsorb U(VI) from aqueous solutions for the first time. Potassium permanganate (KMnO4)-modified FMAR biochar was synthesised, characterised and compared with raw (unmodified) biochar with respect to U(VI) adsorption. The results showed that the adsorption capability of the modified FMAR biochar was evidently higher than that of the raw biochar. Multiple characterisation techniques confirmed that the discrepancy was mainly due to the increased content of O−H and formation of irregular sheet-like nanostructure with the ultrafine MnO2 nanoparticles on the biochar surfaces after KMnO4 modification. The abundance of O−H and nanoscale MnO2 notably enhanced the adsorption of U(VI) by means of coordination and Lewis acid-base interaction. The results indicate that KMnO4-modified FMAR biochar has a good potential to serve as an environment-friendly adsorbent for the removal of U(VI) from solution.

Ultrafine MnO particles embedded in three-dimensional porous g-C3N4/C spheres synthesized through aerosol-pyrolysis route for high energy-density lithium-ion batteries

Ultrafine MnO particles embedded in three-dimensional porous g-C3N4/C spheres synthesized through aerosol-pyrolysis route for high energy-density lithium-ion batteries

Formation of Highly Dispersed Ultrafine MnO2 Nanoparticles on Nitrogen-doped Porous Carbon for Supercapacitor Applications

Formation of Highly Dispersed Ultrafine MnO2 Nanoparticles on Nitrogen-doped Porous Carbon for Supercapacitor Applications

Embedding MnO2 Ultrafine Nanoparticles within Graphene‐Based Hybrid Elastomer as an Anode for Enhanced Lithium Storage

AbstractDespite its high theoretical capacity, the practical application of MnO2 anodes for lithium‐ion batteries is still hindered by poor rate capability, owing to its low electronic conductivity and large volume variation during Li+ insertion/extraction. Herein, these tough issues are tackled by embedding MnO2 ultrafine nanoparticles within polydopamine‐modified reduced graphene oxide. This smart design skillfully utilizes the reduction and self‐polymerization properties of dopamine to reduce graphene oxide while MnO2 ultrafine nanoparticles are embedded in the polydopamine and form a stable interface. The polydopamine, acting as an elastomer, can cushion the stress associated with the expansion of MnO2 ultrafine nanoparticles, and the reduced graphene oxide, as the highly conductive matrix, can greatly improve the rate performance. The resultant composites exhibit a high reversible capacity, excellent cycling stability, and good rate performance, owing to the synergistic effects among conductive graphene, elastic polydopamine, and ultrafine MnO2.

Interconnected network of ultrafine MnO2 nanowires on carbon cloth with weed-like morphology for high-performance supercapacitor electrodes

A binder-free electrode of ultrafine MnO2 nanowires grown on the carbon cloth (CC) were fabricated by simple hydrothermal method, exhibiting the interconnected network with weed-like morphological feature. The unique pore structure has a large interface surface area, and allows rapid electrolyte diffusion through its hollow/open framework and fast electron transfer though the carbon skeleton. As an electrode for supercapacitors, the ultrafine MnO2 nanowires grown on the CC (ultrafine MnO2 nanowires@CC) exhibit a high specific capacitance (1174.3 F g−1 at the moderate current density of 2 A g−1), excellent rate property (stabilize at 927 F g−1 as the current density increases to 40 A g−1), and good cycling stability (a negligible 0.1% decay in specific capacitances after 10,000 cycles).

Ultrafine MnO2 nanowires grown on RGO-coated carbon cloth as a binder-free and flexible supercapacitor electrode with high performance.

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO2 nanowires (CC/RGO/MnO2), forming binder-free and flexible supercapacitor electrode materials. The experimental results indicate that a maximum area-specific capacitance of 506.8 mF cm−2 was gained from the CC/RGO/MnO2 electrode at the current density of 0.128 mA cm−2. Furthermore, the electrode exhibits excellent cycling stability (98.6% specific capacitance was still retained after 10 000 galvanostatic charge–discharge (GCD) tests when the current density was 1.28 mA cm−2). What's more, the area-specific capacitance of the CC/RGO/MnO2 electrode was hardly changed, when the electrode was operated under bending mechanical conditions. In addition, the charge storage performance and mechanism of the MnO2 nanostructures was discussed.

Hierarchical heterostructure of interconnected ultrafine MnO2 nanosheets grown on carbon-coated MnO nanorods toward high-performance lithium-ion batteries

A new hierarchical MnOx-based nanorods consisting of interconnected MnO2 nanosheets grown on carbon-coated MnO nanorod, resembling a unique triple-co-axial heterostructure of MnO2@C@MnO, is successfully designed and prepared by a simple and controllable approach involving subsequent hydrothermal reaction, polydopamine-derived carbon coating and chemical deposition processes. Owing to its unique well-designed architecture with the structural characteristics including interconnected MnO2 nanosheets external wall, self-supported MnO nanorod core, and a high conductivity carbon interlayer sandwiched between them, each component play a critical role for the stable application of this MnOx-based nanocomposite anode toward high-performance lithium-ion batteries. The triple-co-axial MnO2@C@MnO nanocomposite shows excellent lithium-storage capabilities with the high reversible specific capacity of 919.2mAhg−1 at 200mAg−1 after 100 cycles, good rate performance (387.9mAhg−1 at 2Ag−1) and an outstanding specific capacity (1243.2mAhg−1) at the rate of 1Ag−1 after long-term cycles (900 cycles), making it a promising anode material for high-performance lithium-ion batteries.

Porous MnO@C nanocomposite derived from metal-organic frameworks as anode materials for long-life lithium-ion batteries

A novel structure that MnO nanoparticles embedded in a 3D hierarchical carbon matrix (MnO@C) has been successfully synthesized through direct carbonization of metal-organic frameworks. The as-synthesized MnO@C is constructed by ultrafine MnO nanoparticles and porous 3D carbon matrix. Such unique nanoarchitecture can provide 3D continuous transport pathways for the transfer of lithium ions and electrons, and can also alleviate the structural strain during the repeated discharge/charge processes. When evaluated as anode materials for lithium-ion batteries (LIBs), the MnO@C nanocomposite exhibits a high reversible capacity of 1159mAhg−1 at a current density of 100mAg−1 after 50 cycles. And more impressively, a capacity of 613mAhg−1 can retained even at a high current density of 1000mAg−1 after 1000 cycles, indicating that the MnO@C nanocomposite has potential application in LIBs with long cycling life and high power density.

Ultrafine MnO2 Nanowire Arrays Grown on Carbon Fibers for High-Performance Supercapacitors

Large-area ultrafine MnO2 nanowire arrays (NWA) directly grew on a carbon fiber (CF, used as a substrate) by a simple electrochemical method, forming three-dimensional (3D) hierarchical heterostructures of a CF@MnO2 NWA composite. As an electrode for supercapacitors, the CF@MnO2 NWA composite exhibits excellent electrochemical performances including high specific capacitance (321.3 F g−1 at 1000 mA g−1) and good rate capability. Further, the overall capacitance retention is ~99.7 % capacitance after 3000 cycles. These outstanding electrochemical performances attribute to a large number of transport channels for the penetration of electrolyte and the transportation of ions and electrons of electrodes. The as-prepared CF@MnO2 NWA composite may be a promising electrode material for high-performance supercapacitors.

Ultrafine MnO2 nanoparticles decorated on graphene oxide as a highly efficient and recyclable catalyst for aerobic oxidation of benzyl alcohol

The highly active and selective aerobic oxidation of aromatic alcohols over earth-abundant, inexpensive and recyclable catalysts is highly desirable. We fabricated herein MnO2/graphene oxide (GO) composites by a facile in-situ growth approach at room temperature and used them in selective aerobic oxidation of benzyl alcohol to benzaldehyde. TEM, XRD, FTIR, XPS and N2 adsorption/desorption analysis were employed to systematically investigate the morphology, particle size, structure and surface properties of the catalysts. The 96.8% benzyl alcohol conversion and 100% benzaldehyde selectivity over the MnO2/GO (10/100) catalyst with well dispersive ultrafine MnO2 nanoparticles (ca. 3nm) can be obtained within 3h under 383K. Simultaneously, no appreciable loss of activity and selectivity occurred after recycling use up to six times. Due to their significant low cost, excellent catalytic performance, the MnO2/GO composites have huge application prospect in organic synthesis.

MOF-derived ultrafine MnO nanocrystals embedded in a porous carbon matrix as high-performance anodes for lithium-ion batteries

Although MnO has been demonstrated to be a promising anode material for lithium-ion batteries (LIBs) in terms of its high theoretical capacity (755 mA h g(-1)), comparatively low voltage hysteresis (<0.8 V), low cost, and environmental benignity, the application of MnO as a practical electrode material is still hindered by many obstacles, including poor cycling stability and huge volume expansion during the charge/discharge process. Herein, we report a facile and scalable metal-organic framework-derived route for the in situ fabrication of ultrafine MnO nanocrystals encapsulated in a porous carbon matrix, where nanopores increase active sites to store redox ions and enhance ionic diffusivity to encapsulated MnO nanocrystals. As an anode material for lithium-ion batteries (LIBs), these MnO@C composites exhibited a high reversible specific capacity of 1221 mA h g(-1) after 100 cycles at a current density of 100 mA g(-1). The excellent electrochemical performance can be attributed to their unique structure with MnO nanocrystals dispersed uniformly inside a porous carbon matrix, which can largely enhance the electrical conductivity and effectively avoid the aggregation of MnO nanocrystals, and relieve the strain caused by the volumetric change during the charge/discharge process. This facile and economical strategy will extend the scope of metal-organic framework-derived synthesis for other materials in energy storage applications.

Sol–gel process for the synthesis of ultrafine MnO2 nanowires and nanorods

A low-temperature sol–gel process associated with different surfactants in ethanol solvent was applied to prepare ultrafine MnO2 nanowires and nanorods. The surfactants used in the synthesis procedure are crucial for the structure of products. Highly dispersed MnO2 nanowires was formed by assistance of cetyltrimethyl ammonium bromide while hierarchical particles assembled with nanowires were synthesized by usage of pluronic P123 triblock copolymer or Polyvinyl pyrrolidone. The free-standing sheet like structure aggregated with nanorods was obtained by using sodium dodecyl sulfate as a surfactant. All samples were characterized by SEM, TEM, XRD and the results indicated these MnO2 ultrafine nanostructures could be expediently produced by this facile method.